Capacity control with frequency inverter

The average torque at the compressor shaft depends mainly on the operating conditions and the refrigerant and therefore remains virtually constant over a wide speed/frequency range. The cooling capacity and power consumption therefore vary approximately proportionally to the speed (see figure below), and the cooling capacity can be continuously adjusted with the help of the speed. The permitted speeds for Bitzer compressors are documented below.

For safe operation of the compressor with a frequency inverter, it is essential to consider the following limiting factors:

• Minimum and maximum frequency (see below)
• Maximum discharge gas temperature
• Maximum and minimum high pressure
• Maximum operating current of the compressor
• Maximum evaporation temperature

These limiting factors define the application limits for safe operation. However, they may vary depending on frequency ranges and operating conditions. See also chapter Parameters and recommendations for optimal system efficiency and operational safety.

Speed and frequency ranges

Design for other supply voltages and frequencies

If the mains supply deviates from the previously defined standard conditions (400 V/3/50 Hz), special voltage motors and an adapted frequency inverter design may be required (compressor motors). Further information upon request.

Application limits

The following figure shows an example of the application limits of a reciprocating compressor for different frequencies and how they change with the evaporation and condensing temperature. Specific application limits for the respective compressors, motors and refrigerants are listed in the Bitzer software.